Poly(phenylene ether) resin is a type of plastic known for its excellent water resistance, dimensional stability, and inherent flame retardancy. Properties such as strength, stiffness, chemical resistance, and heat resistance can be tailored by blending it with various other plastics in order to meet the requirements of a wide variety of consumer products, for example, plumbing fixtures, electrical boxes, automotive parts, and coated wire.
The reinforcement of rubber compositions with poly(phenylene ether) particles is known. For example, U.S. Pat. No. 3,383,340 to MacCallum et al. describes incorporating poly(phenylene ether) in place of carbon black or inorganic fillers in order to provide a white rubber composition that can take on any desired color. In practice, however, it is difficult to uniformly disperse the poly(phenylene ether) in the rubber composition because rubber compositions are typically blended at temperatures at which poly(phenylene ether)s remain solid. Moreover, to the extent that it is desired to prepare a rubber composition with disperse phase poly(phenylene ether) particles that are smaller than about 35 micrometers in diameter, then the process of preparing the rubber composition would require the use of similarly sized poly(phenylene ether) particles as a starting material, the handling of which in air can create a dust explosion hazard.
U.S. Pat. No. 6,469,101 to Nahmias et al. describes a rubber composition into which is incorporated an organic compound that can be, among others, an amorphous or semicrystalline polymer that is substantially insoluble in the rubber base and exhibits a first or second order transition temperature of from 80 to 160° C. Nahmias abstract. Nahmias discloses that “[o]ptimum results have been achieved with polyphenylenether having a glass transition temperature of 120° C., marketed by Huls under the trade name VESTORAN™ 1100.” Nahmias, column 2, lines 42-45. VESTORAN 1100 is known to be a miscible blend of about 80 weight percent homopolystyrene and about 20 weight percent poly(phenylene ether). Although the low glass transition temperature of 120° C. for VESTORAN 1100 facilitates its blending with rubber, the homopolystyrene/poly(phenylene ether) particles in the resulting rubber would cause the rubber to exhibit an elevated tan delta value at 80 to 140° C., which is predictive of undesirably increased heat build up and increased abrasion in an automotive tire containing the rubber.
U.S. Pat. No. 6,646,066 to Hahn et al. describes rubber compositions with particles of a thermoplastic polymer “selected from at least one of polyphenylene ether, polyphenylene sulfide and syndiotactic polystyrene”. Hahn, column 3, lines 61-62. In the working examples, Example 1, Sample B contains “polyphenylene ether as an alloy with polystyrene”. Hahn, column 5, lines 66-67. The poly(phenylene ether) alloy with polystyrene was obtained as VESTORAN 1900, which is known to have a Vicat softening point of 190° C. Given that the poly(phenylene ether) alloy was blended with the rubber at 165° C., the poly(phenylene ether) alloy remained a solid during that process and was therefore difficult to disperse in the rubber.
Thus, known methods of incorporating poly(phenylene ether) into rubber compositions either utilize a poly(phenylene ether) composition that is a solid under rubber blending conditions and therefore is inadequately dispersed in the rubber composition, or they utilize a poly(phenylene ether) composition that softens under rubber blending conditions and is therefore better dispersed but performs inadequately as a reinforcement in the resulting rubber composition due to the reduced glass transition temperature that facilitated its dispersion. There therefore remains a need for a method of incorporating poly(phenylene ether) into a rubber composition so that the poly(phenylene ether) is well dispersed in the rubber but maintains the high heat-resistance associated with improved performance as a reinforcement.